Refreshing the display when processing

This topic explains when to use the ui.Interface.refresh() method.

The AUI tree on the front-end is synchronized with the runtime system AUI tree, when a user interaction instruction (dialog) gives the control back to the end user.

This means that the end user will not see any changes on the screen, as long as the program is doing batch processing, until an interactive statement is reached and waits for an event triggered by the end user.

To show something on the screen while the program is running in a batch procedure, force AUI tree synchronization by calling the ui.Interface.refresh() method.

Important: The AUI tree is automatically synchronized by the runtime system, when dialog intruction gives the control back to the end user. The ui.Interface.refresh() method must only be used in specific cases, to refresh the display while processing. For example, to show a "Please wait" message, or to implement a progress dialog window with a PROGRESSBAR. The ui.Interface.refresh() method should not be called more often than once in one second.

Example

Form file form.per:

LAYOUT
GRID
{
[pb                              ]
         [b1           ]
}
END
END
ATTRIBUTES
PROGRESSBAR pb = FORMONLY.progress,
                 VALUEMIN=0, VALUEMAX=30;
BUTTON b1: interrupt, TEXT="Interrupt";
END

Program file main.4gl:

MAIN
    DEFINE progress INTEGER
    DEFER INTERRUPT
    OPTIONS INPUT WRAP
    OPEN FORM f FROM "form"
    DISPLAY FORM f
    LET int_flag = FALSE
    FOR progress = 1 TO 30
        IF int_flag THEN
            EXIT FOR
        END IF
        DISPLAY BY NAME progress
        CALL ui.Interface.refresh()
        SLEEP 1
    END FOR
END MAIN